Three and half days is enough to get everything in, but I would do a little planning. You don't need much. Think about what rides they want to do, which ones require fast passes and which ones are important that don't have passes.
You might want to think about which one offers early morning. If you are staying at the park, you can take advantage of it every day, if not, your pass will give you one early morning at DL. We have passes, we we always go the park that does not have early morning, so we can be there at rope drop.
You could do a park a day and have time left over. What are you hoping to do?